402 Big-Block Rebuild, Part 3 - 1967 Chevrolet Chevelle SS

Tech - Real World Street Big-Block, Part 3

Welcome back to our real world street big-block build. If you're just reading about this for the first time, we're rebuilding the 402 Rat that was between the fenders of our rerstored '67 Chevelle when completed by the pros at Auto Metal Direct (AMD) and Craig Hopkins in the AMD Installation Center. The engine had been given a quick teardown and refresh to make sure it was reliable and would move the classic SS396 at idle for shows and events. Now that the car's trailer queen life is over, we needed to tear the 402 apart and get it ready for street/strip duty.

All of our parts are back from the machine shop, and it's time to assemble them. In this installment, we're just going to cover the assembly of the short-block, so we can go a little more in-depth on stuff to better help the novice engine builder out there. In the next installment, we'll cover the assembly of the top end, with special attention being paid to the break-in of our flat tappet camshaft.

For now, let's get our foundation put together.

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1
Before we arrived, Jason had already cleaned the block and given it a fresh coat of high-temp Plasti-Kote Chevy Orange engine paint. This will ensure the engine still looks the part of a stock resto at a glance. The first order of business was installing our cam bearings. This requires a special tool so the bearings are installed squarely in the cam journals, and installed in each journal all the way.

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2 On '67-up big-blocks, all of the cam bearings have holes in them that must be aligned exactly with these holes in the main journals. Oil feeds first through the mains, then to the cam in a big-block. If these holes aren't aligned, the cam bearings, and (after that) top of the engine will be starved for oil.

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3 Before installing freeze plugs, Jason likes to use a thin layer of gasket shellac compound to help seal around the plugs.

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4 Next up is installing the plugs in the oil galley for the cam bearings. Jason likes to drill a small bleeder hole in the front plugs (there's a pair at the back of the block too) to help keep any air in the oil passage bled out so the oil flows freely. Another benefit to this is squirting an extra amount of oil onto the timing chain to help keep it lubed properly.

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5 Moving downward, the main galley plugs were installed. These were holes left from when the block was machined after casting. Jason uses shellac on the threads for sealing on these too.

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6 To add strength to our two-bolt main bottom end, we went with ARP main studs to keep the caps secure. The studs are just hand tightened in at this stage, they'll be fully tightened once the caps are installed and everything is torqued down the first time. Over tightening them now can add stress to the block, and lead to over-torquing/failure of the studs. For those wondering why we didn't seek out a four-bolt main block, the answer is two-fold. First, this is the block we had and there are lots of enthusiasts out there who own them. So, we decided to stick with what we (and they) have. Second, our two-bolt block will be plenty strong enough for our envisioned horsepower levels and use of the car.

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7 To properly find out what our main bearing clearances are, the first step is to use an outside micrometer (mic) to measure the diameter of the main journals on the crank.

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8 The second step is setting an inside mic to the measurement we got from the crank journal.

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9 Before installing our caps, the upper threads on the main studs were coated with ARP's lubricant, included with the main stud kit.

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10 After installing the bearings and caps, all bolts were torque down to factory spec, 110 ft-lbs, in a three step increment of 40-80-110.

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11 Using the inside mic based off the measurement of the main journal on the crank, Jason measured our bearing clearances starting from the back to the front of the block. There will be a natural amount of taper in the mains of a block, so our measurements of .004- , .004- , .00375- , .0035-, and .0035-inch were normal, but a tad on the loose side. The acceptable range of bearing clearance is from .003-.006-inch. You want the clearances as tight as possible without restricting oil flow, but when in doubt (for a street engine) it's always better to err on the looser side for safety and longevity. If your clearances come up out of spec either way, fear not. Bearing companies make different size bearings so you can adjust the clearance within tolerance.

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12 With our bearing clearances checking out OK, we took the caps back off, dropped the crank in place, and torqued the caps back down again. The advantage of using premium fasteners for main and head bolts is you can use them multiple times before distortion from torquing will make them unuseable. In the case of cheap fasteners or “torque- to-yield” bolts, you can only use them once.

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13 With the caps secured, Jason tapped the crank flange to get it aligned properly for checking the crank thrust.

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14 After you've torqued the main caps down, you should be able to spin the crank freely with your hand. If the crank doesn't turn easily, then something's not right, and you need to take everything back apart and check all your clearances again.

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15 Using a dial indicator, Jason moves the crank back and forth to see how much thrust there is. The acceptable range for crankshaft thrust is .003-.008-inches.

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16 Next we get to install our new Lunati mechanical flat tappet cam, part no. 30110512. It specs out at .550 int./.570-inch exh. lift (with a 1.7 ratio rocker), 238/248 duration at .050-inch, and a lobe separation of 112-degrees. Its optimal rpm range is 2,400-6,800 rpm, with a fair idle, and will work well with our 3.73 gears and projected compression near 10:1. It needs a minimum of a 2,500 stall converter, which we'll have once we do the 4L80E conversion to the car.

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17 Before installing the cam, the journals were coated with AMSOIL engine assembly lube, and the lobes with the included moly paste. You don't want to slather the lobes with paste like you were laying bricks, but want enough coverage to protect them during initial start up until the oil pressure comes up before break-in.

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18 For the timing set, we went with Lunati's billet double-roller timing chain, part no. 95510, featuring a nine-way adjustable crank sprocket for a wide range of tuning options. We also got Lunati's cam bolt lock plate kit, so we wouldn't have to worry about our cam bolts coming loose.

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19 With the cam installed, it was time to get our rods ready for mating with their pistons. Our Lunati rods (part no. 70461352) are a 4340 forged steel, H-beam design featuring bushed ends, and cap screw retained caps. Tey are also shot peened and Magnafluxed. Length is stock 402 6.135-inches. These rods will handle just about anything we can throw at our big-block.

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20 Our Lunati rod/Wiseco piston combo utilizes a free floating in design, with the pins retained by spiral locks on each end. To properly install them once the pins are in place, spread the lock apart, then feed it into the piston's lock groove in a wrap-around method. Not hard to do, but it does require a bit of patience. We lubed the pins up before installing them in the pistons and rods.

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21 Time to fit our rings. Wiseco sent us a set of file-fit moly rings for our forged slugs, giving us the ability to get the ring gaps perfectly dialed in, a must for a performance application. To do this, you'll need a ring filer, feeler gauge, and a square. The first step is to get the ring squarely in the cylinder.

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22 Then, using the feeler gauge, measure the gap between the ring ends. Jason likes to leave four thousandths of an inch per inch of bore when setting ring gap. So, in our case, the goal is a .018-inch gap.

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23 Using the ring filer, Jason gently files away a slight amount of ring material, then sets it back in the bore, measures the gap again, and repeats the filing process until he has the desired result. This process is a lot like carpentry, measure twice, cut once. If you file away too much ring material, the gaps will be too big, causing a compression leak in the cylinder and killing performance.

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24 With the ring gaps set, they could be installed on the pistons. Jason advises against using a ring spreader, as they typically overstress and break the rings when used. He installs rings by winding them around the piston into their grooves. First is the oil control ring, followed by the two compression rings. Once installed, clock the individual compression ring gaps 180-degrees apart, with the gap for the oil control ring between the two.

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25 With the piston and rod assemblies set, it was time to check our rod bearing clearances. The same method used for the main bearings is used here. Jason likes to see the bearing clearances on the rods fall between .003- and .005-inch.

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Using the inside mic, and based off our rod journal measurement from the crank, our bearing clearance was at .005-inch, on the loose side but still within spec.

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27 With that done, we could install the piston/rod assemblies. After putting some oil on the cylinder walls and ring compressor, the assembly is slipped through the ring compressor, and gently tapped into the cylinder. Always be careful when doing this so you don't nick the cylinder walls with the uncapped rod ends.

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28 After installing everything, we turned the block over to install our oil pump. We went with a standard Melling M-77HV (high volume) oil pump from Summit Racing. With our clearances on the loose side, we felt comfortable using the high volume pump on our street engine. In applications where a HV pump is used in a street engine with tight tolerances, the increased pressure can blow the oil right off the bearing surfaces, meaning they don't have the proper amount of oil to prevent wear. Consult with your engine builder or the manufacturer if you're unsure which volume pump to use. We also used the corresponding Melling oil pump driveshaft.

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29 Jason likes to pull new oil pumps apart and check their insides for any casting flash that could break off during operating and get sucked into the motor to cause damage. Once he's made sure it's clean (ours was fine), he uses this special tool to install the oil pump pickup.

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30 Big-blocks use three different depth oil pump pickups. Starting with a standard one, Jason measures from the bottom of the oil pan to its flange. Then he goes to the block, and compares his measurement with the location of the pickup. Enough clearance has to be left so the oil pump can suck oil through in high enough quantities to feed the engine. To get the right clearance, you either have to change pickup lengths, or simply rotate the pickup enough to get the proper clearance while keeping the pickup immersed in oil.

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31 Once we had the pickup clocking set, Jason tack welded it in place.

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32 Next up was installing our windage tray. A windage tray keeps the crankshaft from frothing up the engine oil, which restricts oil flow, along with creating parasitic drag on the crankshaft. The windage tray also helps with oil baffling to keep the oil in the sump area of the pan during acceleration and cornering. We used a standard Moroso big-block windage tray form Summit Racing, part no. 23030. The first step is setting the lower nuts the will set the tray's depth.

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33 Next, Jason sets the tray down and adjusts the lower nuts till the tray is level and clears the crankshaft throws.

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34 Once the depth is set, the top nuts are tightened down, securing the tray.

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35 When using studs or bolts with provisions for a windage tray, you have to check their depth in the pan to make sure they don't hit. With no gasket installed, our studs were hitting the baffle on the oil pan. Easily solved. Using the marks the studs had made, Jason used a drift and hammer to tap reliefs in the baffle to clear the studs. After that, the pan sat flush (without gasket) and had no clearance issues/

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36 And there you have it. Our short-block is assembled (minus oil filter adapter and filter) and ready for the top end of the engine. In our next installment, we'll cover that, and the proper method for breaking in a flat tappet cam. Stay tuned!

In the last issue, we covered the disassembly of the 402 big-block out of our AMD 1967 Chevelle. In Part 2 of Real-World Street Big-Block, we reassemble and rebuild our 402 big block. In this installation, we start off by cleaning all of the parts in order to get it ready for assembly. » Read More